STROBE Statement—checklist of items that should be included in reports of observational studies

Title and abstract

ItemNo1

Recommendation(a) Indicate the study’s design with a commonly used term in the title or the abstract(b) Provide in the abstract an informative and balanced summary of what was done
and what was found

Introduction
Background/rationale

2

Explain the scientific background and rationale for the investigation being reported

Objectives

3

State specific objectives, including any prespecified hypotheses

Methods
Study design

4

Present key elements of study design early in the paper

Setting5

Describe the setting, locations, and relevant dates, including periods of recruitment,exposure, follow-up, and data collection

Participants

6(a) Cohort study—Give the eligibility criteria, and the sources and methods of
selection of participants. Describe methods of follow-up
Case-control study—Give the eligibility criteria, and the sources and methods ofcase ascertainment and control selection. Give the rationale for the choice of casesand controls
Cross-sectional study—Give the eligibility criteria, and the sources and methods of
selection of participants(b) Cohort study—For matched studies, give matching criteria and number ofexposed and unexposed
Case-control study—For matched studies, give matching criteria and the number ofcontrols per case

Variables

7

Clearly define all outcomes, exposures, predictors, potential confounders, and effectmodifiers. Give diagnostic criteria, if applicable

Data sources/measurement

8*

For each variable of interest, give sources of data and details of methods ofassessment (measurement). Describe comparability of assessment methods if there
is more than one group

Bias

9

Describe any efforts to address potential sources of bias

Study size

10

Explain how the study size was arrived at

Quantitative variables

11Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why

Statistical methods

12(a) Describe all statistical methods, including those used to control for confounding(b) Describe any methods used to examine subgroups and interactions(c) Explain how missing data were addressed(d) Cohort study—If applicable, explain how loss to follow-up was addressed
Case-control study—If applicable, explain how matching of cases and controls wasaddressed
Cross-sectional study—If applicable, describe analytical methods taking account ofsampling strategy(e) Describe any sensitivity analyses

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Results
Participants

13*(a) Report numbers of individuals at each stage of study—eg numbers potentially eligible,
examined for eligibility, confirmed eligible, included in the study, completing follow-up, andanalysed(b) Give reasons for non-participation at each stage(c) Consider use of a flow diagram

Descriptive
data

14*(a) Give characteristics of study participants (eg demographic, clinical, social) and information
on exposures and potential confounders(b) Indicate number of participants with missing data for each variable of interest(c) Cohort study—Summarise follow-up time (eg, average and total amount)

Outcome data

15*

Cohort study—Report numbers of outcome events or summary measures over timeCase-control study—Report numbers in each exposure category, or summary measures ofexposure
Cross-sectional study—Report numbers of outcome events or summary measures

Main results

16(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and theirprecision (eg, 95% confidence interval). Make clear which confounders were adjusted for andwhy they were included(b) Report category boundaries when continuous variables were categorized(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningfultime period

Other analyses

17

Report other analyses done—eg analyses of subgroups and interactions, and sensitivity
analyses

Discussion
Key results

18

Summarise key results with reference to study objectives

Limitations

19

Discuss limitations of the study, taking into account sources of potential bias or imprecision.
Discuss both direction and magnitude of any potential bias

Interpretation

20

Give a cautious overall interpretation of results considering objectives, limitations, multiplicity
of analyses, results from similar studies, and other relevant evidence

Generalisability

21

Discuss the generalisability (external validity) of the study results

Other information
Funding
22

Give the source of funding and the role of the funders for the present study and, if applicable,
for the original study on which the present article is based*Give information separately for cases and controls in case-control studies and, if applicable, for exposed andunexposed groups in cohort and cross-sectional studies.
Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background andpublished examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freelyavailable on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at
http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative isavailable at www.strobe-statement.org.

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